Protecting workers from heat-related injury or stress is very important in most modern companies. For example, for employees working near blast furnaces and steam generators, in foundries, or in enclosed areas, it is very important that personal cooling devices be available to reduce the risk of heat stress. In general, these personal cooling devices take the form of garments that are worn by the workers. The garments provide ventilation by supplying a flow of air near the worker's body. One of the major expected benefits of such garments is that they provide a steady flow of moving air or some other cool gas near or next to the surface of the skin of the wearer. Another major expected benefit is that these devices are portable and have lightweight construction. Finally, as the temperature changes, the flow rate of gas can be monitored, and adjusted to keep the worker comfortable.
U.S. Pat. No. 4,738,119, by P. Zafred and assigned to Westinghouse Electric Corp., discloses a device for enhancing personal comfort in the form of a garment having outer and inner linings stitched together, with a plurality of tubes disposed between the inner and outer linings. A charge of liquefied carbon dioxide must first be delivered under high pressure into the tubes. The carbon dioxide is converted to a solid phase in the tubes and eventually sublimes to gaseous carbon dioxide, which escapes through micropores in the tubes.
Another such device is described in U.S. Pat. No. 5,303,425 to P. Mele. This patent describes a generally helical tubular structure attached to the inner portion of a garment. The tubular structure has discrete expansion points disposed at spaced intervals. These expansion points are inflated, for example by blowing into one end of the tube, and the garment is lifted away from the wearer's skin to allow increased air circulation next to the skin.
Still another type of cooling device is described in U.S. Pat. No. 5,255,390 to S. Gross et al. The patent shows a gas-ventilated garment with a plurality of radial dispersion valves positioned at various locations and connected to receive air at a pressure of 20 to 125 pounds per square inch. Each valve releases ventilating air against the skin at low pressure and in a radial direction, thereby achieving cooling.
Although the above-noted cooling devices and similar devices are capable of producing a cooling effect, they are of limited efficiency and are generally complex. None of these devices takes full advantage of the principle known as the "Coanda effect". This principle of fluid flow was first described in U.S. Pat. No. 2,052,869 to H. Coanda. The Coanda effect is achieved by the discharge of a small volume of fluid under high velocity from a nozzle having a shaped surface adjacent to it. The stream of fluid (referred to as the "primary fluid") tends to follow the shaped surface and induces surrounding fluid (referred to as the "secondary fluid") to flow with it. The result is a stream of fluid consisting of both the primary and secondary fluids, and a flow-multiplying effect in which of a relatively large amount of secondary fluid is moved by a comparatively small volume of primary fluid.